Accurate diagnosis of solid pediatric tumors requires a combination of diagnostic techniques including reverse transcription polymerase chain reaction (RT-PCR). Many pediatric solid tumors exhibit fundamental cytogenetic abnormalities that have implications in their pathogenesis. The Ewings sarcoma family of tumors (ESFT) and alveolar rhabdomyosarcoma (RMS) are characterized by consistent chromosomal translocations which result in the fusion of genes and subsequent formation of novel chimeric genes. These molecular markers can be detected by RT-PCR or fluorescence in situ hybridization (FISH) and can be used not only to establish the diagnosis in difficult cases, but also to understand the pathogenesis of these tumors. Recently, the products of these fusion genes have become the target of vaccine therapies in newly established protocols in the Pediatric Oncology Branch (POB) at the NCI. The objective of this project is: (1) to provide state of the art diagnosis of solid pediatric tumors (2) to assist in the evaluation of pediatric tumor specimens for the presence or absence of specific fusion transcripts and (3) to evaluate the significance of molecular markers in the diagnosis, classification and pathogenesis of pediatric sarcomas. The following accomplishments have been made in the last year: (1) A total of 150 Pediatric Pathology reports were issued. (2) A total of 90 RT-PCR reports were issued. (3) A series of 50 pediatric sarcomas were evaluated by RT-PCR and conventional methods. The study showed that RT-PCR is needed for diagnosis in selected cases and should be interpreted in conjuction with the morphlogic findings (4) FISH is a very useful technique to detect fusion products in paraffin sections (5) Olfactory neuroblastoma is negative for the EWS/Fli-1 fusion transcripts by FISH, in contrast to the ESFT. (6) Microsatellite markers at the tyrosine hydroxylase locus in chromosome 11p are helpful in the distinction of RMS from other spindle cell sarcomas, but not in the distinction of alveolar from embryonal RMS. - Pediatric sarcomas, RT-PCR, molecular markers, - Human Tissues, Fluids, Cells, etc.